The present invention relates generally to optical switches and, more particularly, to the novel employment of fiber lens assemblies in singlemode optical switch designs.
Optical switches are commonly used in optical communication networks to switch an optical signal from one path to another. In one form of optical switch to which this invention is directed, optical waveguides or fibers terminate within a switch body where mirror elements are moveable to switch the optical signal path from input fibers in order to redirect the optical signal path to one or more output fibers.
An exemplary optical switch is disclosed in U.S. Pat. No. 4,932,745 to Blonder, assigned to ATandT, the disclosure of which is incorporated by reference herein in its entirety. In this ""745 patent, an optical switching arrangement has a mirror which is positioned either out of an optical path or in an optical path to deflect optical signals between input and output fibers. The switching arrangement has first, second, third and fourth optical ports which are formed by respective proximate ends of first, second, third and fourth optical fiber segments disposed in respective grooves etched or otherwise formed in, for example, a silicon substrate base. The switching arrangement further comprises first, second, third and fourth lenslets that serve to collimate the respective optical beams emanating from the first fiber, entering into the second fiber, or entering into the third or fourth fibers. Optical radiation for these optical beams is supplied by a light source (not shown) and is collected in a known manner. The mirror has a frontal planar reflecting surface and may also have another reflecting surface parallel thereto, such as a rear planar reflecting surface.
As mentioned above, the foregoing switching arrangement can be integrated into a silicon workbench technology assembly in order to form an optical switching assembly. This optical switching arrangement may be employed in an optical switch 10 disclosed, for example, in FIGS. 1, 2 and 5 of the instant application in which there is depicted an exemplary electromagnetic-based activation mechanism 12 used to actuate movement of the mirror 14 (normally biased with a spring 16) through a spring to switch optical signals traveling along one of incoming optical waveguides 18a disposed within the substrate switching base 20. More specifically, with reference to FIG. 1, the substrate base 20 typically has a major planar surface 22 in which first, second, third and fourth waveguide alignment grooves 24a, 24b, 24c, and 24d are formed to receive the respective optical fibers 18a, 18b, 18c and 18d. A respective lens alignment recess (e.g. of pyramidal shape) 26a, 26b, 26c and 26d is disposed at the respective end of each waveguide groove 24a-24d (see FIG. 1) to receive a ball lens 28 (FIG. 2) to collimate the incoming (18a) or outgoing (18d) optical beam. A simple optical beam switching or rerouting is achieved by moving the mirror 14 into a beam deflecting position (in which the incoming path (18a) is deflected to a non-aligned outgoing fiber (18d)) or a non-deflecting position in which the incoming beam passes into an aligned outgoing beam 18c after passing through both collimating lens 28 respectively associated therewith. While the illustrated switch design is a 2xc3x972-switch configuration, the present invention has applicability to 1xc3x971, 1xc3x972 and other higher order matrix switch configurations as well.
Since the light rays are collimated and transmitted across a gap from one fiber 18a and 18b through their associated pair of lenses 28 which focuses the light to the receiving fiber 18c and 18d, it is extremely important that the fiber optic mounting grooves 24a-24d and lens mounting recesses 26a-26d be machined to provide a high degree of alignment and thereby eliminate insertion losses occurring as a result of, for example, dimensional variations in the respective grooves/lens mounting recesses that otherwise impede the ability of the entire signal to be transmitted between fiber ends as a result of misalignment.
The foregoing optical switch designs work generally well with multimode fibers that are typically of large diameter (e.g. 50 micrometer cores) since the dimensional variations that exist between the fiber optic mounting grooves 24a-24d and ball mounting recesses 26a-26d are generally insufficient to give rise to unacceptable insertion losses given the relatively large core diameter of the multimode fiber. However, in the case of singlemode fibers in which the cores are much smaller than the multimode fibers (e.g. singlemode fiber cores are typically 8-10 micrometers), insertion losses are unacceptably high with the foregoing switch design since the dimensional variations between the fiber mounting and lens mounting recesses 24a-24d and 26a-26d that were acceptable for multimode switches are unacceptable for singlemode switches. From FIG. 2, it is apparent that four sources of dimensional variation exist which are lens diameter, lens pocket dimensions, fiber diameter, and V-groove dimensions. If only one of these dimensions is out of tolerance, this variation or misalignment will produced misalignment in the entire system.
It is accordingly an object of the present invention to improve the design of singlemode optical switches to minimize insertion losses.
Another object is to improve singlemode optical switches that utilize singlemode collimators to configure higher order matrix switch designs while maintaining acceptable low insertion losses.
Another object is to design a singlemode optical switch having insertion losses as low as 0.3 dB for 1xc3x971, 1xc3x972, and 2xc3x972 switch configurations.
Another object is to manufacture a singlemode optical switch with fewer dimensional tolerances that would otherwise cause rejection of manufactured product.
The present invention concerns an optical switch utilizing a reflecting element to redirect optical signals between a plurality of different singlemode waveguides. The singlemode optical waveguides are mounted to a switch substrate wherein at least one of the waveguides is an input waveguide and another of the waveguides is an output waveguide. In accordance with the invention, each waveguide has a separate collimating lens section attached directly to an endface of the waveguide, advantageously eliminating dimensional variations and misalignment that would otherwise occur by mounting separate collimating lens within the switch substrate as known in the prior art.
The optical fiber switch with the fused fiber lens assemblies fused directly to the singlemode fibers may have m-input/n-output fibers for 1xc3x971, 1xc3x972, and 2xc3x972 switch configurations, as well as other higher order matrix switch configurations while maintaining acceptable low insertion losses.
Insertion losses are kept to a minimum since the plurality of waveguides are respectively disposed in grooves formed in the switch substrate with the associated lens formed in the same groove eliminating the need for separate lens receiving pockets that disadvantageously give rise to dimensional variation.
In the preferred embodiment, each collimating lens is preferably a multimode fiber attached to the end of the singlemode fiber. A preferred form of attachment is fusion splicing.
The multimode fiber lens is a graded index multimode fiber that may have a step index section fused directly to the singlemode fiber end.
Since the collimating fiber lens assemblies according to the invention are short lengths of fiber (e.g. graded index or graded index and step index) which have been fusion spliced to the end of the single mode fiber, use of the smallest collimators advantageously allows the physical dimensions of the optical switch to be reduced to a minimum so that the switch or multiple switches may be attached to a circuit board or be placed in an enclosure with a minimum of volume. This is an extremely important consideration for the telecom and datecom industries.